Kitz Forum

Broadband Related => Telephony Wiring + Equipment => Topic started by: H4rry on January 24, 2017, 12:11:04 PM

Title: Does anyone have a spare BT80A-RF2 ?
Post by: H4rry on January 24, 2017, 12:11:04 PM
Does anyone have a old BT80A/RF2? (Or know where I could source one? no listings on ebay at the moment) I need one in order to prove a concept that a local AM radio mast is causing interference on the telephone line.

The latest RF3 is no good for the test as it lets through DSL signals which overlap the same frequency as AM radio and therefore will not filter out the RFI.
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: burakkucat on January 24, 2017, 04:02:22 PM
Welcome to the Kitz forum, H4rry.  :)

Hmm . . . Sorry but I do not have one in my grotto.  :no:

A year or so ago I remember assisting Walter (http://forum.kitz.co.uk/index.php?action=profile;u=1253) in sourcing such a device and eventually an eBay seller was found.

Ah, ha! Here's one (http://www.ebay.co.uk/itm/391684518017).  :)
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: 4candles on January 24, 2017, 04:18:15 PM
Good work b*cat.  :)

The seller is lucky to find a buyer as

"GPO Strowger Block Terminal 80b used to help Filter out Radio Interference"

doesn't mention 'RF2'.

Still, the photo confirms it's the right article.
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: burakkucat on January 24, 2017, 04:25:29 PM
Good work b*cat.  :)
. . .
Still, the photo confirms it's the right article.

It was a case of tingles in the whiskers, coupled with the thought that I had recently seen one listed, that prompted me to scrutinise the image.  ;)
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: H4rry on January 24, 2017, 05:20:28 PM
Thanks burakkucat you are a star! :)

If anyone else has (or knows of) one immediately available please let me know as the auction still has 8 days to run.

Thanks again
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: burakkucat on January 24, 2017, 05:28:33 PM
Thanks burakkucat you are a star! :)

  :blush:
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: ejs on January 24, 2017, 06:08:19 PM
What about using an ordinary DSL microfilter? The phone socket on a microfilter would have all the DSL (and AM radio) frequencies filtered off.
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: H4rry on January 24, 2017, 06:48:36 PM
I thought the same thing ejs

I tried a microfilter but still got the interference. There's no DSL on the line so I wondered whether the microfilter, being passive, needed an active DSL service to work. As such, I've also placed an order for a high quality active microfilter (xf-1e) (which contains a transistor based ciruit powered by the line) in order to try again and see whether that will filter out the AM radio station (which incidently is GOLD on 1548KHz).

Between that and an RF2 I'm hoping one or the other will work, otherwise it's back to the drawing board scratching my head.
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: tubaman on January 24, 2017, 07:44:11 PM
Have you tried a different phone on the line, as it could be the phone circuitry that's picking up the AM rather than the line itself.
 :)
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: H4rry on January 24, 2017, 08:25:53 PM
Im sure tried 3 different phones, connected to test socket, 95% of the time it's a perfect line, then all of a sudden sounds like tuner control being twisted and gold radio coming and going. I am now on the 5th BT engineer visit that just runs a test on the line at times when line is fine and leaves marking the case as resolved. Decided to take a more hands on approach before calling BT out again.
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: NewtronStar on January 24, 2017, 09:19:36 PM
Had a look in my large Broadband cupboard and have two BT80A RF3 units and quite unsure why the RF2 would be any better than the RF3 in your case as both have a ferrite toroid with windings inplace for ADSL and VDSL frequency range

You want all the DSL signals to reach your modem and not to be filtered out I would not even use the BT80A RF2 or RF3 if you already have a SSFP installed at the master socket
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: H4rry on January 25, 2017, 05:39:50 AM
I don't have a modem it's just a plain pots line without DSL.

The RF2 filters out more than the RF3 so hoping it will filter out the AM radio sounds that are coming through on 1548khz which the RF3 may let slip through since DSL frequency range also covers that frequency. Its just a theory which is why I'd like to try it out and see.

I've just sourced an RF2 and placed the order.

Fingers crossed the RF2 or microfilter will work.
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: burakkucat on January 25, 2017, 06:04:03 PM
Essentially you would require a low-pass filter suitable for the range DC - 4 kHz. For added efficiency, a parallel LC tuned circuit (1548 kHz) could be added as a shunt across the pair.

fresonant = (2 Pi (LC)-2)-1      (1)

Rearranging (1) gives . . .

LC = (fresonant2 4 Pi2)-1      (2)

Substituting known values into (2) . . .

LC = 1.057 x 10-14 Henry Farad
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: H4rry on January 25, 2017, 07:26:11 PM
:) That's going beyond my understanding burakkucat.

However, if my efforts of introducing the components I've ordered don't resolve the problem I will make a cup of tea, pull out my old physics and electronics reference books, pull up comfy chair and try and understand your equation for using a low-pass filter with a shunt.

This forum is great :)
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: tubaman on January 26, 2017, 09:22:28 AM
This is odd as a normal DSL dongle should fix this as it should filter out everything above approx 4KHz.
Admittedly the cut-off won't be perfect but it certainly should be killing frequencies as high as 1548KHz.
 :hmm:
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: H4rry on January 26, 2017, 12:54:35 PM
I thought that when I put in the passive ADSL filter but then wondered if DSL being absent was preventing the filter from doing it's job... It may be the case that the RFI could be coming from another source... through AC wiring maybe. In which case, if the RF2 and active filter don't fix matters I am going to go systematically through all nearby wiring and maybe introduce some ferrite rings to see if that helps.
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: burakkucat on January 26, 2017, 06:23:13 PM
Although we do not know of your location and the immediate topography, I am assuming you are not located near the top of a hill with direct line of sight to the aerial of the relevant broadcast transmitter.

I wonder, on what type of telephone do you experience that RF breakthrough?  :-\
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: H4rry on January 27, 2017, 08:33:27 AM
No, situated in North London 6 miles from the transmitter (Saffron Green Mast).

I'm starting to get the feeling that this is a mains power problem. I think there's an AC adaptor somewhere picking up the radio station and then feeding it through the power wiring.

What confused me though, was that I completely shut down the house power from the master switch on the consumer unit, connected to the master socket test port and still got the rfi, but it wouldn't happen as often as when on the extension wiring. The very fact that it happened at all on the providers wiring with no power connected (using a simple corded telephone - no psu) is what has thrown me and I have been drawing my attention away from the local environment...

I'm running Quiet Line Tests when I can and systematically changing things until I hit on it... It can't hide forever :)
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: Dray on January 27, 2017, 11:02:19 AM
Is your phone wiring using twisted-pair, because untwisted will enable rfi?
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: H4rry on January 27, 2017, 11:58:42 AM
Yep, twisted pair all the way, I disconnected the bell wire from the master socket a few days ago since that is not part of a balanced pair and wondered if it was the culprit. Unfortunately not.
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: burakkucat on January 27, 2017, 05:02:53 PM
Ah, Saffron Green [1][2]. Unfortunately you are situated in the target location, specified to receive the broadcast transmissions!

[1] http://tx.mb21.co.uk/gallery/saffrongreen/
[2] http://wiki.tx.mb21.co.uk/index.php?title=Saffron_Green
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: H4rry on January 27, 2017, 06:05:09 PM
Yep, right in the firing line...

The RF2 arrived but it hasn't made any difference [sigh].

I've done more Quiet Line Tests via the test port and the interference is there even after unplugging the surrounding power cables. This problem is happening on BT's side. I told the initial engineer that the interference started when Broadband was removed from the line but he said that is likely to be a coincidence.

The most frustrating problem I am facing is that it's an intermittent interference that only happens about 5% of the time. When an engineer shows up there's no way to ensure that it will be happening and most engineers so far have arrived run HR/PQ/AC etc tests and just said that the line is fine and left. The only engineer to have made any changes was the initial one that changed pairs from the cab to the exchange after finding that it failed a PQ test at the cab and then came back to the house where it failed again but subsequently passed on a further test so off he went.

I've booked a further engineer for Monday.

Since the RF2 did not filter it out I'm now wondering if the RFI is happening at the exchange and then encoding it before I receive it? If it was in it's analogue form wouldn't the filter handle it? Listening to the interference it's not a continuous radio station but rather flashes of a station (always GOLD though).

I've attached a (zipped) mp3 of a typical quiet line test whilst the interference is happening. This was recorded today, it lasted for an hour and then disappeared again.

[attachment deleted by admin]
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: burakkucat on January 27, 2017, 06:21:00 PM
The RF3/RF2 are constructed for common-mode rejection, i.e. to reject spurious signals that appear on both legs of the pair. If the pair shows poor AC balance then common-mode rejection will be degraded.

Listening to your sample mp3 file, I noticed a brief heterodyne whistle. (Silly question time: Exactly how, with what, did you make that recording?)

I'm now leaning towards the possibility of a developing HR fault at a joint or at least a joint that is starting to show semi-conductive tendencies. Such a non-linear joint would obviously rectify any induced RF and also be the source of all sorts of intermodulation products.
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: H4rry on January 27, 2017, 06:36:56 PM
I see, so an imbalance on the lines (maybe due to a sudden HR fault - damp?) would prevent the said filters from filtering properly.

I made the recording using an ATA via an Asterisk PBX.

I'm hoping the engineer that comes on Monday is UG certified. Hopefully he can change pairs from the house DP to the cab (D-Side?) whereby I think that would constitute a complete change of all pairs to the exchange and hopefully resolve any HR fault along the path.
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: burakkucat on January 27, 2017, 06:48:42 PM
I see, so an imbalance on the lines (maybe due to a sudden HR fault - damp?) would prevent the said filters from filtering properly.

Yes, that is a possibility.

Quote
I made the recording using an ATA via an Asterisk PBX.

Ah, I understand. So that particular quiet line test was not performed from the test socket with nothing but a basic wired telephone connected. (I like to know all the details so as not to make any false deductions.)

Quote
I'm hoping the engineer that comes on Monday is UG certified. Hopefully he can change pairs from the house DP to the cab (D-Side?) whereby I think that would constitute a complete change of all pairs to the exchange and hopefully resolve any HR fault along the path.

Yes, that is the D-side of your circuit. Do you have an underground service-feed to your property? Or is it via a final aerial drop?
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: H4rry on January 27, 2017, 07:20:22 PM
Yes, the quiet line test attached was via the ATA however it is indicative of tests done via the corded phone in the test socket.

I have a handheld recorder I could use next time I have the interference happening via a simple corded phone in the test socket.

The house is served via an underground service-feed. (no aerial-drop)

Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: burakkucat on January 27, 2017, 09:05:20 PM
So the first joint, Openreach side of the NTE5/A, may be under a grey capping (or something similar), low on the external wall of the house. That one is always worth a (visual) look . . . just a few screws to undo.

The next joint will probably be at either an underground DP or just where your service feed connects to the larger D-side cable. And so on, to the PCP.
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: H4rry on January 28, 2017, 03:15:14 PM
The block terminal has already been checked, I got excited when I saw that there was green corroded contacts hoping that was the cause. But, after cutting back and re-terminating, the problem was no different. Btw, is the block terminal (grey capping) sometimes referred to as the DP? (Distribution Point) or is that label reserved for the branch of connectors under the first pavement cover?

I'm going to ask the engineer that arrives on Monday to change the connectors up to the PCP and hope that will sort it.

I've made another recording today (attached) that was done on a handheld mp3 recorder held next to the earpiece of a plain and simple corded telephone plugged into the master test socket. All other devices where unplugged.
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: burakkucat on January 28, 2017, 04:03:10 PM
. . . is the block terminal (grey capping) sometimes referred to as the DP? (Distribution Point) or is that label reserved for the branch of connectors under the first pavement cover?

The distribution point would be the latter for an underground feed. If an aerial feed was being considered, the DP is the terminal block at the top of the pole from whence all subscribers' drop-cables fan out to each property.

Quote
I've made another recording today (attached) that was done on a handheld mp3 recorder held next to the earpiece of a plain and simple corded telephone plugged into the master test socket. All other devices where unplugged.

Having listened to it, it does sound as if there is one (or more) defective joint(s) . . . HR or semi-conductive (non-linear).
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: H4rry on January 28, 2017, 05:52:10 PM
Thanks for your invaluable input burakkucat. I'm guessing former BT Engineer?.... or if your avatar is anything to go by, taste tester at Whiskas or Bird Catcher.
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: burakkucat on January 28, 2017, 09:29:24 PM
I'm guessing former BT Engineer?....

No, not ex-Openreach, not ex-BT, not ex-PO Telephones nor ex-GPO.

Just someone who took an interest in such things, back in the days when GPO employees were members of the Civil Service (i.e. before October 1969).  :)
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: tickmike on January 28, 2017, 11:20:21 PM
Your recordings do sound like a HR joint (as I have one under investigation by BT at the moment) but because you are near that transmitter it is acting like a old type of 'Cats Whisker' crystal radio set and picking up that strong signal.
I have a iphone and that has a 'Voice memo' app that I have recorded some of the crackles of the bad joint on a QLT.
If you do a QLT 17070 / 2 and after she says goodbye, wait for the tone, wait until it finishes, then after the tone you can get a period of the line without her saying QL test every 30 sec. 
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: H4rry on January 29, 2017, 09:58:24 AM
@burakkucat
You come from a great place, when people cared more and had to actually know and learn something to get ahead in life. Nowadays companies seem more concerned with cutbacks to achieve numbers on a report that engineers do bare minimum to achieve rather than putting in the time to fix a customer's problem. But why would they when they are not incentivised... anyhow I digress :)

@tickmike
Yep I think we're in the same boat. Although mine is accompanied by radio to soothe my suffering. I tried your suggestion but my phones seem to react to the said tone and immediately disconnect the line. That's fine though, the interference is abundantly frequent and clear between the announcement and a QLT call lasts about 5mins 30secs for me.

Would be great to hear how you're getting on with your progress. I'll keep posting updates my end.
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: H4rry on February 08, 2017, 09:37:56 AM
Phew what an ordeal!

After being stood up last Monday and then being promised a UG certified engineer on Tuesday only to receive another internal engineer and subsequent persevering and suffering FINALLY an engineer arrived that found the problem to be a badly corroded pair behind the block terminal on the side of the house.

The block terminal contacts were cut back and re-terminated by a previous engineer but those wires where also corroded on their way to the contact behind the terminal block casing. Yesterday's engineer completely removed the terminal block and replaced with a simple enclosure in which he terminated the contacts with jelly crimps. This not only makes a better contact than a screw terminal it also waterproofs the contacts so the corrosion that lead to the noise shouldn't return.

The line is now crystal clear and Quiet Line Tests have never sounded better.

So, I think I can now safely conclude (famous last words) that the HR fault was due to the corroded contacts behind the terminal block causing a HR/semi-conductive fault on the line that was acting like a 'cats whisker' radio introducing noise on the line.

Thanks to all who commented, especially burakkukat.
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: tubaman on February 08, 2017, 10:17:34 AM
Great news  ;D
Intermittent faults are rarely quick to get sorted as the law of sod says that they don't show themselves when you want them to.
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: tickmike on February 08, 2017, 11:52:32 AM
That's a great result,  I have a feeling that my line problem will be sorted soon  ;D
After sending an email to the CEO of BTOR last night I think the Brown stuff has hit the fan this morning from the emails I am getting from high up within BT and BTOR about it.
http://forum.kitz.co.uk/index.php/topic,19162.30.html
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: H4rry on February 08, 2017, 01:26:23 PM
@tubaman
I was banging my head on a wall each time an engineer was turning up only for the noise to disappear when plugging the butt tester in. I think there must be a scientific element to Sod's law :)

@tickmike
I've had exactly the same experience, it wasn't until I lodged a complaint and escalated the case that things started to happen. It seems that the 'normal' process of reporting a fault is not where intermittent faults like ours are taken seriously. Good luck with your case, sounds like the right things are happening towards a fix. If you happen to have an old wall block terminal with screw terminals it might be something to look closer at.

I'm still doing QLT in the background... Sod's law has often taught me that things can also be 'too good to be true'. 20 or so QLTs later though and still smiling...
Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: 4candles on February 08, 2017, 01:31:21 PM
Nice to hear some good news.   :)



Title: Re: Does anyone have a spare BT80A-RF2 ?
Post by: burakkucat on February 08, 2017, 04:05:08 PM
And I'll second 4c's post!  :)

It's nice to read of an "at last" resolution.  :thumbs: